1. Field of the Invention
The present invention relates to a level conversion circuit, and is applied, for example, to a level conversion circuit of a semiconductor circuit.
2. Description of the Related Art
In the prior art, for example, a level conversion circuit, which is applied to a semiconductor circuit, is configured to have only a positive-side level conversion unit. Thus, in the conventional level conversion circuit, level conversion of only a positive-side output level, relative to an input level, is executed, and a negative-side output level is a ground voltage (VSSL). As a result, there is a tendency that an output voltage difference of the level conversion circuit is small.
In addition, the conventional level conversion circuit is configured such that a maximum output potential difference between a positive level and a negative level (i.e. high power supply voltage VDDH−ground voltage VSSL) is constantly applied across a current path of an output transistor. Consequently, in the case where the output transistor is fabricated by the same fabrication process as other transistors that constitute the level conversion unit, etc., an output amplitude, which is greater than a breakdown voltage across the current path of the transistor, cannot be obtained. The reason is that the breakdown voltage across the current path of the output transistor is determined by the fabrication process.
On the other hand, in order to perform large-amplitude output voltage conversion, it is necessary to increase the breakdown voltage of only the output transistor, thereby to withstand the large-amplitude output voltage that is applied to the output transistor. In this case, however, a fabrication process for increasing the breakdown voltage of only the output transistor is additionally required, leading to an increase in the number of fabrication steps and in manufacturing cost.
As described above, in the conventional level conversion circuit, if the output voltage difference is to be improved, there is a tendency that an overvoltage, which is higher than the breakdown voltage, is applied to the transistor that constitutes the output unit.
Jpn. Pat. Appln. KOKAI Publication No. 11-88147 is an example of documents relating to the present invention. Jpn. Pat. Appln. KOKAI Publication No. 11-88147 discloses an example in which a MOS transistor with a high breakdown voltage is made needless by lowering a voltage which is applied to the MOS transistor that is used.